This invention relates to a rear arm pivot structure for a motorcycle and more particularly to an improved motorcycle frame and rear wheel suspension thereof.
The importance of providing a light weight, compact and yet high strength frame and suspension arrangement for a motorcycle are well known. These problems are particularly acute due to the high stresses under which motorcycles may be driven, particularly in such activities as moto-crossing or the like.
One popular form of suspension for the rear wheel of the motorcycle employs a trailing arm that is pivotally supported at its forward end by a lower rear portion of the frame and which carries the rear wheel at its rear end. Substantially all of the suspension loadings for the rear wheel are transferred to the frame through this rear pivot joint. Obviously, therefore, the rear pivot joint must be capable of withstanding high loads and with previous motorcycle constructions, this has been difficult.
In addition, to these problems, it is also desirable, when utilizing a chain drive for driving the rear wheel, to have the axis of rotation of the driving sprocket be aligned with the pivot axis of the trailing arm. By so orienting the drive sprocket and the pivot arm axis, the effect of change of length of the driving chain during suspension travel can be minimized. However, such a location then requires a rather wide frame arrangement at the lower end and this is clearly undesirable.
Furthermore, when the drive for the rear wheel is positioned coincident with or close to the pivot axis of the rear wheel trailing arm, then servicing of the drive arrangement and specifically the driving sprocket and chain can be difficult.
It is, therefore, a principal object to this invention to provide an improved frame and trailing arm construction for a motorcycle that will have high strength, compact construction and yet will afford ease of serviceability.
It is a further object to this invention to provide an improved frame structure for a motorcycle embodying a trailing arm suspension wherein the frame is constructed in such a way that the loading of the rear wheel on the frame will be well absorbed.
It is a still further object to this invention to provide a rear wheel trailing arm suspension arrangement for a motorcycle wherein servicing of the components associated with the drive of the rear wheel can be facilitated.
In connection with one popular form of rear wheel trailing arm suspension, loads are transferred from the trailing arm to the suspension element of the rear wheel through a linkage system that is connected to the trailing arm between its pivot point and the point of journal for the rear wheel. As such, bending loads are applied to the trailing arm which can cause deflection and/or permanent damage. If, however, the trailing arm is made strong enough to absorb all of these loads and have a generally uniform configuration, then the total trailing arm weight becomes excessive.
It is, therefore, a still further object to this invention to provide an improved trailing arm arrangement for the rear wheel of a motorcycle that is light in weight and yet high in strength.